An anode of nickel-hydrogen rechargeable batteries which are currently produced in a large amount is mainly produced with an Mm (misch metal) --Ni--Co--Mn--Al alloy of AB.sub.5 type. This alloy has the properties of larger hydrogen storage capacity than other alloys, and a usable hydrogen absorption-desorption pressure of 1 to 5 atmosphere at ordinary temperature.
However, conventional AB.sub.5 type rare earth metal-nickel alloy has drawbacks of expanding and contracting due to the absorption and desorption of hydrogen, thereby generating cracks and being pulverized to deteriorate the electrical properties thereof.
Alternatively, electrodes having still larger electrical capacity are demanded. In order to increase the electrical capacity of electrodes, an alloy has been developed having a composition wgherein the atomic ratio of transition metals containing nickel as a main ingredient to rare earth metals is 4.5 to 5:1, thereby increasing the content of rare earth metals.
However, the electrical capacity of this alloy is increased at a sacrifice of the long life. This alloy also has a drawback in that in mass-producing the alloy of such composition through a conventional melting method and a mold casting method, segregations rich in rare earth metals tend to be formed, which can be a starting point of cracks and corrosion.
For the purpose of preventing the formation of such segregations rich in rare earth metals, Japanese Laid-open Patent Application No. 2-220356, for example discloses a method for producing a homogeneous alloy by injecting an alloy melt onto a copper roller rotating at a high speed to rapidly quench and solidify the alloy melt. Further, Japanese Laid-open Patent Application No. 6-73466 discloses 2 to 5 hour-annealing of an alloy which has been rapidly quenched and solidified at 550 to 950.degree. C. in vacuum or an inert gas atmosphere for releasing cooling strain occurred by the rapid quenching and solidification. According to these two methods, improvements in the homogeneity of the alloy, as well as corrosion resistance and cell life are recognized.
However, sufficient improvement in electrical capacity is not recognized by the above method. Therefore, an alloy which achieves both high electrical capacity and long life is not practically known yet.
By the way, it is an accepted theory that a rare earth metal-nickel alloy having the above-mentioned AB.sub.5 type structure does not have a solid solution range (T. B. Massalski et al.: Binary Alloy Phase Diagrams, Vol. 2. 1468 ASM (1986)). Also, an AB.sub.6 type rare earth metal-nickel alloy containing fine precipitated phases in the crystal grains thereof is not known. Still less, it is not known that such fine precipitated phases can be a factor of improving both electrical capacity and cell life when the above-mentioned alloy is used in the anode of a nickel-hydrogen rechargeable battery.